The present invention relates to improved cellulosic paper sheets or synthetic paper sheets having improved sharpness when used with inkjet printers. More specifically, this invention relates to inkjet printable sheets having improved properties. This invention also relates to a coated type ink jet recording sheet. More particularly, it relates to a coated type ink jet recording sheet for use in an ink jet recording system that employs water-base inks. The product of the instant invention exhibits a high rate of absorption of the ink deposited on the recording sheet so as to allow a clear color to develop, providing an image having circular dots and sharply defined edges, having a high surface strength and the same touch and feel during use as plain paper, and being able to record images with high resolution that are water-proof. The ink jet recording sheet of the present invention may be used in recording, printing and writing employing water-base ink. The sheet of the present invention can be a cellulosic paper, a transparent sheet derived from synthetic polymers or any substrate which is usable in printing operations.
The present invention also relates to a recording sheet, and more particularly to an inkjet recording sheet prepared from a cellulosic support such as paper, on which there is applied a coating providing superior image performance. This invention relates generally to transparencies, and more specifically the present invention is directed to transparencies with certain coatings thereover and the use of these transparencies in ink jet printing processes.
The history of improving the print quality of paper is based on the need to get the color to stay where it is applied. This need coincides with a need for the ink to dry as rapidly as possibly due to higher printing speeds. Current technology has been to apply a particulate, usually silica, to the paper surface to act as small dams in order to get the ink to go into the sheet of the paper and not spread out on the surface. If the ink spreads on the surface, the sharpness of the image becomes degraded due to the ink vehicle carrying the color with it. This is called xe2x80x9cfeatheringxe2x80x9d in the print paper industry. So if the paper sheet remains fairly hydrophilic and absorbent, feathering occurs easily. One approach to the problem is to make the surface more hydrophobic. The problem here is that the inks do not dry as rapidly if they are sitting on a hydrophobic surface and there is a need for solvent based inks for faster drying. This is something that is not desirable from an environmental standpoint and the ink manufacturer""s have been trying to move away from this.
In order for an ink jet recording system to be able to produce high quality recorded images, it is required that the substrate employed be such that the ink deposited on the surface of the recording sheet i.e., paper spreads to form a true circle and is absorbed quickly in a controlled manner without becoming irregularly spread on the surface, and that the surface structure be such as to promote coloration of the deposited ink.
In order to improve the capacity to absorb ink and to provide a higher ink absorption rate and that spreading of the ink may be controlled so as to realize a dot shape close to a true circle without adversely affecting the water-proof quality and the color brightness, it is necessary to drastically increase the amount of specialty coating materials coated on the substrate surface to a value not less than 10 g/m2. With a coating amount of not more than 10 g/m2, the dot shape and coloration are not satisfactory and the dot size control that is necessary for good quality image reproduction cannot be achieved. However, if the coating amount is increased, the cost of the paper is raised and the feel of the plain paper and its suitability for use may not be acceptable.
Non-coated type ink jet paper has recently become popular in view of its suitability from the standpoint of cost, printing quality and adaptability to use as office paper. It is known with regard to the production of such ink jet papers to add for example liquid-absorbing pigments such as silica or heavy calcium carbonate at the time of making the paper. However, this type of ink jet paper presents certain problems in that the ink may not develop sufficient color brightness when applied to and absorbed by the paper on account of certain optical properties of the pulp and filler customarily used so that a clear coloration of a quality comparable to that obtained when using coated paper is not attainable. Furthermore spreading of the ink cannot be prevented and the ink absorption rate and capacity are low.
For applications in which importance is attached to the brightness of color images, a coated type of paper is employed which has a coating layer consisting essentially of white pigments having superior water absorption properties so that the above-described dot shape and color brightness can be obtained. In the absence of a specialized type of processing, it is impossible to provide water-proof images if water-base ink is used with any of these types of paper.
The most successful inkjet recording sheets presently in use employ non-cellulosic polymer supports because of their exceptional smoothness. However, as the use of inkjet printers becomes more widespread, there is a growing need for developing inkjet sheets using cheaper and more economical substrates such as paper. The use of paper as a substrate for an inkjet recording sheet provides both advantages and disadvantages. One obvious advantage is cost, but another advantage is the ability of the paper to absorb the ink vehicle rapidly during printing. The main disadvantage is a lack of smoothness as compared with non-cellulosic, polymer substrates.
Inkjet systems are comprised of three components, the printer, the ink and the recording sheet. The printer controls the size, number and placement of the ink droplets and contains the transport system. The ink provides the colorants which form the images, and the recording sheet provides the medium or substrate which accepts and holds the ink. The quality and archivability of ink jet prints is a function of the total system. However, the composition and interaction of the ink and the recording sheet affect the quality and archivability of the imaged product.
There are two primary requirements for inkjet printing. The first is that the coating, and the substrate in the case of paper supports, must be absorbent enough to immobilize the vehicle of the inks so that the inks will not smear permitting fast ink drying and high printing speeds. The second requirement is that the coating provide a means for keeping the dyes in the inks on the surface of the sheet with minimal spreading, tailing or blurring of dots to provide a sharp image. If the dyes are not kept on the surface of the sheet the colors could fade since the dyes will become diluted by the high light scattering ability of the preferred pigments used in inkjet coatings.
Fast drying properties have been achieved in the past by incorporating silica or other large specific surface area pigments in the inkjet recording layer so as to increase ink absorption. However, an inkjet recording layer with a pigment of large specific surface area provides a surface having low smoothness. As a result, the appearance of the image deteriorates and the reproduction of the image becomes unsatisfactory. Enhanced smoothness can be achieved, however, by calendering or supercalendering the inkjet recording sheet, but this action tends to destroy the porosity of the inkjet recording layer resulting in a decrease in the ink absorption and reduced drying properties. Nevertheless, emphasis in the prior art has dictated the use of nonflake-like pigments for use in inkjet coatings. Nonflake-like pigments include calcium carbonate, silicas, calcined clays and other such pigments whereas flaky pigments include clays, talc and mica.
Typical binders for inkjet coatings disclosed in the prior art are water soluble polymeric binders including polyvinyl alcohol, polyvinyl alcohol copolymers such as poly (vinyl alcohol-co-vinyl acetate), hydroxypropyl cellulose, acrylic resins such as poly (methyl methacrylate/ethyl acrylate/acrylic acid), sodium alginate, water soluble phenol formaldehyde resins, carboxylated styrene butadiene polymers, carboxymethyl cellulose, hydroxyurethanes, soluble collagen gelatin, hydrolyzed ethylene vinyl acetate polymers, and polysaccharides such as xanthene gum, gum tragacanth, locust bean gum, guar gum, and agur, etc. Also noted in the prior art are aqueous dispersions of poly(vinylpyrrolidone), vinylpyrrolidone-vinyl acetate copolymers, or mixtures thereof.
Although the papers currently used by the consumer are suitable for their intended purposes, there remains a need for papers with new coatings that are useful in ink jet printing processes, including color processes, and that will enable the formulation of images with high optical densities. Additionally, there is a need for treated papers that can be selected for ink jet color printing processes. Another need resides in providing papers the fibers of which are coated continuously with certain polyester compositions as illustrated herein. There is also a need to provide papers for ink jet, dot matrix, typewriters and crayon printing processes, and wherein images of high optical density, such as greater than one, are obtained in some embodiments of the present invention.
In accordance with the present invention, novel coating formulations have been discovered which utilizes many of the components disclosed in our prior U.S. Pat. No. 4,977,191 but which produces superior image performance when applied to a paper substrate and printed with an inkjet printer.
The present invention is characterized by careful selection of water soluble and dispersible polyester materials to achieve a high level of success.